1. Field of the Invention
The present invention relates to the field of utilizing a robot to process and assemble small work-pieces having small parts or components while in a pallet held by the robot end effector. More particularly, the present invention relates to how processing tools may be advantageously fixed to the last arm of the robot while the end effector can rotate with respect to the robot arm. Most particularly, the present invention is highly advantageous when arrays of parts are held on the end effector in rotatable pallets which are rotated and moved vertically with respect to the sensors and devices fixed to the robot arm.
The present invention permits the robot to accomplish tasks by passing the work-pieces in front of the sensors and devices that are commonly needed for robotic processing tasks as soon as the pallet is picked up, during transit to a work-station, as part of the actions of the work-station, and prior to setting the pallet back down upon completion of the tasks.
2. Description of the Prior Art
Since the term part can be highly confusing in the following text, the term "work-piece" is defined as a part that is being worked on by the robot, or a component of such a work-piece or a smaller pallet that retains a work-piece. In the art of automatic assembly and processing equipment, a nest is something that retains a work-piece. The nest can be a simple hole, a machined, fitted block of material, or a more complex device including devices which wedge or hold the work-piece. Grippers are devices which actively hold the work-piece and typically permit the work-piece to fall when the grip is released. Selective compliance articulated robot arm (SCARA) robots are a class of industrial assembly robots that may hold a work-piece rigidly in the Z axis (vertical) while permitting the robot arm to move easily in the horizontal X and Y directions.
Commonly in automatic assembly and processing machines, as soon as a work-piece is placed on an assembly, the gripper moving the work-piece confirms that a work-piece was gripped by means of a sensor in the gripper, or at the next operating station at which a photocell verifies the presence or condition of the assembly. Such sensing is necessary to enable the machine to stop when incomplete or defective assemblies are being made at high speed.
In prior art robotic processing modes, the robot is primarily used as a programmable pick-and-place between a supply of components and an assembly or to use the robot to move a single or multiple-headed tool about a work-piece. These robots have gripper sensors to verify successful gripping and placement of parts.
A very common SCARA robot used for industrial small parts assembly is disclosed in U.S. Pat. No. 4,702,668 issued to Carlisle et al. on Oct. 27, 1982 (hereafter "the Carlisle Patent"), which is available commercially as the Adept One robot.
It is common in the art to have a CCD camera mounted on the end of the last arm of the robot and by having the robot arm move the camera to an advantageous position to precisely locate a work-piece not then held by the robot in preparation for pick up by the robot, or to verify the correct positioning of a work-piece previously placed by the robot.
The following prior art references are relevant to the field of the present invention.
1. U.S. Pat. No. 4,741,078 issued to Kimura on May 3, 1988 for "Multi-Function Industrial Robot" (hereafter "the Kimura Patent"). PA0 2. U.S. Pat. No. 4,438,309 issued to Zimmer on Mar. 20, 1984 for "Tool Holder For Manipulator Arm" (hereafter "the Zimmer Patent"). PA0 3. U.S. Pat. No. 4,740,133 issued to Kawano on Apr. 26, 1988 for "Composite Working Device Using A Robot And Method Of Accomplishing Composite Work Using A Robot" (hereafter "the Kawano Patent"). PA0 4. U.S. Pat. No. 4,880,265 issued to Drexel et al. on Nov. 14, 1989 for "Robot Arm With An Assembly Flange For Tools" (hereafter "the Drexel Patent"). PA0 5. U.S. Pat. No. 4,995,148 issued to Bonomi et al. on Feb. 26, 1991 for "Robotically Controlled Multi-Task End Effector" (hereafter "the Bonomi Patent").
The Kimura Patent discloses a tool carrier which rotates 45.degree. off the vertical axis so that only the tool directly below the robot head is in use. The Kimura Patent permits a robot to utilize several different small tools, but only one small tool at a time and not while it also carries the work-pieces on which it is operating. The robot is of a special, dedicated design atypical of SCARA robots. The tool carrier is not removable as an assembly, but individual tools are removable.
The Zimmer Patent discloses a tool holder. The tool holder is a working tip of the end effector, which in this case is a spot welding tip. The spot welding tip is mounted on the end effector and is driven by a bevel gear to rotate about a horizontal axis. Rotating a central meshing bevel gear causes the welding tip to rotate in the transverse (horizontal) axis so that the tip can be pointed at any angle with respect to the end effector. The novel part is the arrangement for commutation of electrical power and cooling fluids through the tips which is accomplished by contactor shoes bearing on a cylindrical surface fixed to the robot end effector. As the end effector is rotated 360.degree. about a vertical axis, the commutator also rotates. Flexible electrical cables connect the tool holder to the commutator ring to permit the rotation about the transverse axis.
The Kawano Patent discloses a large 6-axis welding robot welding automobile doors. It includes a spot welding head and a first joint member in the form of a hook that is used to move a fixture holding the semi-complete door in a tooling frame to different stations. The hook is simply a parallel tool on the end effector. The hook is used to move the work, but not when the robot is welding on it.
The Drexel Patent discloses a flange mounted between the robot end effector and a primary tool in line with the robot wrist. Additional tools can be mounted to the end effector on each of the four sides. The robot would use one and then use the other. The robot moves the tool, not the work.
The Bonomi Patent discloses two 6-axis robots which cooperate together to drive rivets in aircraft panels without releasing their pressure on the panels. The robot end effector on the left provides the backup to the rivet insertion operations. The robot end effector on the right has a central quill that can be driven and rotated. The tools are carried in the linear apparatus which is moved across in front of the quill as necessary to complete all of the drilling and riveting operations.
In all prior art cases, the robot was being used more efficiently in the prior art modes of either picking up and placing a part or in using a tool then acting directly under the wrist axis of the robot to perform work on work-pieces not supported by the robotic head.
A co-pending patent application Ser. No. 08/189,118 filed on Jan. 26, 1994 by the same inventor (hereafter "the '118 Application"), discloses a method and apparatus for processing and assembly of small work-pieces utilizing a robot wherein the work-pieces are held in nests which are primarily in circular arrays on a rotatable pallet that the robot grips, rotates, elevates and lowers while it moves the pallet through a plurality of processing stations. The '118 Application created a situation wherein the present invention could be used for further improving the speed of robots assembling small parts while reducing the cost and complexity of the robotic processing cell. The work-piece arrays of the '118 Application can also be linear arrays of work-pieces arranged on straight sides of the rotatable pallet. The work-pieces on the rotatable pallets can be pallets containing linear arrays, or lead frames containing linear arrays.
As used in Japan, the term robot includes a wide variety of devices such as simple pneumatic pick-and-place with mechanical end stops. It may also be applied to dedicated machines having an operating head with a vertical stroke and separately able to move work-pieces in the X and Y directions relative to the head by means such as linear and crossed-axis, motor driven slides.
The disadvantages with the prior art devices are that the tools on the robot head move with the end effector and no tools are provided for working on the work-pieces while they are being held and moved by the end effector. The "118 Application rotatable pallet carries small parts away from the centerline mechanisms of the robot head now enabling useful work to be performed by tools on the robot head at work-stations arrayed around the robot work-envelope and during transit between the work-stations.